Leetcode: Reverse Words in a String II

Given an input string, reverse the string word by word. A word is defined as a sequence of non-space characters.

The input string does not contain leading or trailing spaces and the words are always separated by a single space.

For example,
Given s = "the sky is blue",
return "blue is sky the".

Could you do it in-place without allocating extra space?

Code (Java):

?

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41

public class Solution {     public void reverseWords(char[] s) {         if (s == null || s.length <= 1) {             return;         }                   int i = 0;         int j = s.length - 1;         while (i < j) {             swap(s, i, j);             i++;             j--;         }                   // Step 2: swap again within a token         i = 0;         j = 0;         while (j < s.length) {             while (j < s.length && s[j] != ' ') {                 j++;             }                           int m = i;             int n = j - 1;             while (m < n) {                 swap(s, m, n);                 m++;                 n--;             }                           i = j + 1;             j = i;         }     }           private void swap(char[] s, int i, int j) {         char tmp = s[i];         s[i] = s[j];         s[j] = tmp;     } }